Control system for transmission

ABSTRACT

An engine drives a vehicle through a transmission that incorporates clutches and planetary gearing together with a hydraulic drive unit that variably and reversibly drives a reaction component of the planetary gearing for stepless changes through a series of ranges of vehicle speed. The driver shifts a control handle through positions corresponding to the series of ranges and a control system for the transmission includes servomeans that operates at a predetermined rate to automatically vary the hydraulic drive unit and to engage the various clutches in accord with the changing positions of the control handle.

United States Patent [191 Olsen et al. 6

CONTROL SYSTEM FOR TRANSMISSION [451 July 10,1973

3,580,107 4/l97l Orshansky, Jr. 74/687 [75] Inventors: Gerald N. Olsen, Torrance; Arthur washbum, Anaheim both of Primary Examiner-Arthur T. NlcKeon Calm Attorney-Smyth, Roston & Pavitt [73] Assignee: White Motor corporation, [57 ABSTRACT Cleveland Ohlo An engine drives a vehicle through a transmission that [22] Filed; D 7, 1970 incorporates clutches and planetary gearing together with a hydraulic drive unit that variably and reversibly [21] Appl 95820 drives a reaction component of the planetary gearing for stepless changes through a series of ranges of vehi- [52] US. Cl. 74/687, 74/3375 ele p The driver t a ntr l handl thr ugh [51] Int. Cl. ..'Fl6h 47/04, Fl6h 5/06 positions p d ng t t s ri s of ranges and a 58 Field of Search 74/687, 337.5 control System for the transmission includes servomeans that operates at a predetermined rate to auto- [56] Referen es Cit d matically vary the hydraulic drive unit and to engage UNITED STATES PATENTS the various clutches in accord with the changing posi- 3,293,943 12/1966 MacDonald 74/687 of the control handle 3,489,036 1 1970 Cockrell et a]. 74/687 24 Claims, 25 Drawing Figures 4 C 5.5 30 75a e 9 e 6 Patented July 10, 1973 3,744,344

15 Sheets-Sheet 5 417 a 1' Zerai'aee/ Fun 9 Patented July 10, 1973 3,744,344

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Patented July 10, 1973 15 Sheets-Sheet l5 1 CONTROL SYSTEM FOR TRANSMISSION BACKGROUND OF THE INVENTION The invention relates to a continuously variable powered transmission of the general type set forth in the Gunderson et al. U.S. Pat. No. 3,427,899, which patent is hereby incorporated into the present disclosure by reference. The Gunderson transmission, which is especially suited for tractors, incorporates planetary gearing, a hydraulic drive unit for variably and reversibly driving the sun gear of the planetary gearing and further includes seven clutches to provide various paths of power flow through the transmission. An improvement on the Gunderson et al. transmission disclosed in a copending application by Robert B. Singer, Ser. No. 879,390, now US. Pat. No. 3,626,787 filed Nov. 24, 1969, adds a second sun gear and a second set of planet gears to make it possible to reduce the number of clutches from seven to four.

Although power flow is transmitted trhogh such a transmission in a stepless manner, the overall speed capability is divided into a series of speed ranges, the hydraulic drive unit being operated in different modes for the different ranges. To shift from range to range, the operating mode of the hydraulic unit must be changed, and where different combinations of clutches are employed in successive ranges, the stepless operation requires that clutches be operated in an overlapping manner for the transition from range to range. It is apparent that the manipulation of the various controls of the transmission for various changes in the vehicle speed is complicated and would place a heavy burden on a tractor operator who needs to be free to place his attention elsewhere. It would be only too easy, moreover, to damage the transmission structure by improper or untimely manipulation of the controls.

In addition to the need for simplifying the manual procedure for controlling the transmission there is need for suitable provision for stopping the vehicle in an emergency. It is to be borne in mind that if need for an emergency stop occurs when the tractor is in high speed, the clutches involved for that speed should be kept engaged for an initial period of retardation of the tractor by the engine.

The broad object of the invention is to provide such a control system in which both the sequential operation of the clutches and the sequential adjustments of the hydraulic drive unit may be made by manual movement of a single master control and abrupt stops may be made by a single emergency control.

SUMMARY OF THE INVENTION A fluid-pressure-actuated control system including means to vary the adjustment of the hydraulic drive unit of the transmission means to activate the various clutches is energized by a pump that is driven directly by the engine. For emergency stops, the invention employs the rate of output of the pump to sense when the vehicle speed drops sufficiently to warrant release of the clutches. A single manually operable master control is shiftable out of neutral in one lateral direction to a realtively long slot where the lever may be moved forward through three speed ranges or may be moved rearward through a low speed reverse range. The master control may also be shifted from neutral in the opposite lateral direction to a short slot for a high speed reverse range.

The control system includes a first program means to program the required adjustments of the hydraulic drive unit through the ranges of speed of the vehicle and the control system further includes a second program means that is synchronized with the first program means and is movable through a series of positions corresponding to the series of speed ranges of the vehicle to program the engagement and disengagement of the four clutches as required. In the preferred embodiment of the invention, the master control is manually movable by the operator independently of the two program means and servo means causes the two program means to seek positions corresponding to the instant positions of the master control. The preferred embodiment of the invention further includes means to control the rate at which the two program means follw the changes in position of the master control.

The first program means for controlling the adjustment of the hydraulic drive unit comprises a program cam having a control surface that rises and falls to change the adjustment of the hydrostatic drive unit, the slope of the control surface of the cam being in accord with the desired gain control, i.e., change in vehicle speed per unit movement of the cam. The cam has a dwell at the transition between the first and second forward speed range and has a dwell at the transition between the second and third forward speed ranges, the

two dwells providing time for the required overlapping of the clutch operations.

The four clutches are activated by fluid pressure and the second program means comprises a program valve which is preferably in the form of a rotary commutator valve to operate the various clutches in the desired sequence. In this regard a feature of the invention is the concept of using two spool valves for the four clutches. The spool of each valve operates two of the clutches alternately by movement of the spool to its alternate limit positions, both clutches being engaged when the spool shifts through a central position. Each spool valve is spring-centered and sufficient fluid pressure is available at both of its ends to overcome the spring pressure. By virtue of this arrangement the program valve may change clutches by simply venting the two ends of the two spool valves selectively.

Two of the four clutches are engaged in each speed range and the same two clutches are used for the low speed reverse range as for the first forward speed range so that it is not necessary to disengage the clutches and go into free wheeling at the transition between these two ranges. This feature makes it possible to inch the vehicle either forward or rearward from zero speed by simply easing the master control forward or rearward while the two clutches are engaged.

At the transition between the first and second speed ranges and again at the transition between the second and third speed ranges, clutches are operated by the program valve in overlapping manner, a third clutch being engaged before one of the two clutches is released. Thus the three clutches are momentarily engaged simultaneously to make possible uniterrupted power flow during the transition.

In the preferred embodiment of the invention the operator has the choice between a low speed reverse range in which the planetary gearing of the transmission is operated differentially and a high speed reverse range in which two of the clutches lock up the planetary gearing for rotation as a unit. A feature of the invention is that the movements of the program cam and of the clutch program valve that are employed for the high speed reverse range are the same movements that are employed for the first range of forward speed. When the master control is shifted to its high speed reverse range the program cam and the program valve both respond by taking positions they normally use for the first forward speed range but means responsive to the shift of the master control intervenes to substitute a combination of clutches that is different from the combination of clutches that is normally used in the first forward speed range.

When the master control moves forward through the first speed range, the program cam also moves forward. It is highly desirable, however, that the master control be moved manually rearward through the high speed reverse range instead of being moved manually forward because rearward movement of the master control is natural to the operator for a reverse speed range. Thus it is desirable that the program cam move forward both in response to forward movement of the master control in the first forward speed range and in response to rearward movement of the master control in the high speed reverse range. The invention solves this problem by providing reverse gearing which reverses the response of the cam to the master control when the master control is shifted laterally from neutral position to its rearward path of movement for the high speed reverse range.

As will be explained, the invention provides various safeguards in the operation of the vehicle. One safeguard disables clutches to insure that the vehicle is in free wheeling whenever the master control is in its neutral position. Another safeguard releases the clutches whenever the engine is stalled and insures that the clutches stay released until the master control is returned to a zero speed position. Another safeguard provides for quick stop of the vehicle in an emergency. If the vehicle is traveling at a relatively low speed when the emergency occurs, all of the clutches are immediately automatically released but if the vehicle is traveling at a relatively high speed when the emergency occurs, the automatic release of the clutches is delayed sufficiently to permit the inertia of the engine to assist in the intitial deceleration of the vehicle.

The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative: f

FIG. I is a diagrammatic view of the physical structure of the presently preferred embodiment of the transmission separate and apart from the transmission control system;

FIG. 2 is a diagram of the transmission shown in FIG. 1, the diagram showing the clutches that are engaged for the first range of forward speed, the same clutches being employed for low speed reverse;

FIG. 3 is a similar diagram showing the clutches that are engaged for the second forward range of speed;

FIG. 4 is a similar diagram showing the clutches that are engaged for the third forward speed;

FIG. 5 is a similar diagram showing the clutches that are engaged for high speed reverse;

FIG. 6 is a diagram showing the changes in speed and the changes in rotation of the various components of the planetary gearing throughout the various speed ranges and further showing the clutches that are engaged for the different speed ranges;

FIG. 7 is afragmentary face view of a cam which serves as a programmer to program the adjustments of the hydraulic drive unit in its two opposite respects for the speed ranges that are indicated in FIG. 6;

FIG. 8 is a perspective view of a manually operable master control and the associated linkage that are employed in the preferred embodiment of the control systern;

FIG. 9 is a perspective view of an emergency stop pedal and associated linkage employed in the control system;

FIG. 10 is a perspective view showing the location of a lockout pin to prevent premature shift of the master control into the high speed reverse range;

FIG. 11 is a diagrammatic view showing the construction of the outkout pin;

FIG. 11a is a simplified sectional view of valve G in FIG. 12;

FIGS. 12 21 are diagrammatic views of the control system in its various modes of operation, the face of the cam being opposite from the face shown in FIG. 6;

FIG. 22 is an exploded view of a servo-positioner employed in the control system;

FIG. 23 is a fragmentary diagrammatic view indicating the construction of a modification of the control system; and

FIG. 24 is a fragmentary diagrammatic view indicating the construction of another modification of the control system.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION THE TRANSMISSION APART FROM THE CON- TROL SYSTEM In FIG. 1 which shows the structure of the presently preferred embodiment of the transmission separate and apart from the control system, an input shaft 30 is permanently mechanically connected by a pair of gears 31 to a first motor-pump 32, which in turn, is hydraulically connected to a second motor-pump 34 by a pair of conduits 35. The two motor-pumps 32 and 34 together constitute an infinitely variable hydraulic drive unit which is reversible in the direction of power flow and is also reversible in output direction without reversal of input direction.

Each of the motor-pumps 32 and 34 is of the axialpiston type and motor-pump 32 has a cylinder block 36 that is tiltable in a well known manner relative to a drive flange 38 for variation in volumetric displacement to vary the speed of the second motor pump. The cylinder block 36 has a center position for zero speed of the second motor pump 34 and may be swung in opposite directions from its zero speed position to actuate the second motor pump in opposite directions. Thus the first motor pump 32 may be adjusted to actuate the second motor-pump 34 at various speeds in either rotary direction. The second motor-pump 34 operates constantly at maximum displacement.

The hydraulic drive unit is combined with a planetary gear assembly that includes a first sun gear 40, a ring gear 42, a planet gear carrier 44 and a set of planet gears 45 mounted on the planet gear carrier 44. For

input power flow to the ring gear 42 the ring gear is provided with external input teeth 46 which are in mesh with a gear 48, the gear 48 being rotatably mounted on the input shaft 30. The planetary gearing further includes a second sun gear 50 and a second set of planet gears 52'on the planet gear carrier 44, the second set of planet gears being in mesh both with the second sun gear 50 and with the first set of planet gears 45.

The planet gear carrier 44 is permanently connected to the output shaft 54 of the transmission. The input shaft 30 and the second motor-pump 34 are releasably connected to various parts of the planetary gearing at different stages in the operation of the transmission system. For this purpose four clutches are provided which are designated A, B, C and D.

Clutch A releasably connects the gear 48 to a tubular shaft 55 that surrounds the input shaft 30. The tubular shaft 55 carries a gear 56 that is in mesh with a gear 58 that is freely rotatable on the shaft 60 of the first motorpump 32 independently of the first motor pump. A gear 62 is freely rotatable on a shaft 64 that carries the second sun gear 50 and the gear 62 is not only in mesh with the gear 58 but is also in mesh with a gear 65 that is keyed to the shaft 66 of the second motor-pump 34. It is apparent that engaging clutch A releasably connects the second motor-pump 34 to the ring gear 42 by activating a gear train that includes gears 65, 62, 58, 56 and 48.

Clutch B releasably connects the gear 62 to a tubular shaft 68 that surrounds the shaft 64 and carries the first sun gear 40 and thus releasably connects the second motor-pump 34 to the first sun gear. Clutch C releasably connects the input shaft 30 to the gear 48 and thus releasably connects the input shaft to the ring gear 42. Clutch D releasably connects the gear 62 to the shaft 64 that carries the second sun gear 50 and thus releasably connects the second motor-pump 34 to the second sun gear.

How the four clutches A D are variously used in the different speed ranges may be understood by reference to the diagrams in FIGS. 2 5 and reference to the chart in FIG. 6, in all of which the first sun gear 40 is designated 5, and the second sun gear 50 is designated 5 In FIGS. 2 5 the clutch connections to the various parts of the planetary gearing are shown diagrammatically and FIG. 6 indicates the directions of rotation and the relative speeds of the different components of the planetary gearing throughout the series of speed ranges. FIG. 6 also indicates the sequence in the operation of the four clutches in the series of speed ranges. Note that FIG. 6 shows transition stages between the first and second speed ranges and between the second and third speed ranges with overlapping operation of clutches indicated in each transition.

In both the first forward speed range and in the low speed reverse range, both of which are represented by FIG. 2, the second motor-pump 34 is connected by clutch A to the ring gear 42 and is also connected by the clutch B to the first sun gear S to cause the first sun gear and the ring gear to rotate in opposite directions. With the vehicle standing still and with the tiltable cylinder block 36 of the first motor-pump 32 at its center position for zero displacement, the input shaft 30 is rotated by the vehicle engine at maximum speed without transmitting power to the planetary gearing. To start transmission of power, the cylinder block 36 of the first motor-pump 32 is progressively tilted in one direction to accelerate the ring gear 42 in one direction for the first forward speed range or the cylinder block is progressively tilted in the opposite direction to accelerate the ring gear in the reverse direction for the low speed reverse range. Since the clutches A and B are both engaged when the cylinder block is at its zero speed, the vehicle may be inched either forward or rearward by simply slightly swinging the cylinder block out of its center position.

At the upper end of the first or lowest forward speed range where the first motor-pump 32 is operating at full displacement, both of the two motor-pumps operate at the same speed to make possible a transition to the second forward speed range by overlapping clutch operation without interrupting the power flow to the output shaft 54. To make this transition clutch C is engaged while clutches A and B are engaged and then clutch A is disengaged to leave the two clutches B and C engaged.

Assume that at the start of the second forward speed range when clutches B and C are both engaged as shown in FIG. 3 and as indicated in FIG. 6, the first sun gear S is rotating counterclockwise at maximum speed and the second sun gear S is rotating clockwise at maximum speed. To progress through the second speed range, the counterclockwise rotation of the first sun gear S and the clockwise rotation of the second sun gear S are both decelerated to zero at the mid point of the range. To progress through the upper half of the speed range from the mid point, the two stationary sun gears S and S are both progressively accelerated in the clockwise direction. Thus to carry out the full extent of the second forward speed range the cylinder block 36 of the first motor pump 32 is progressively tilted from one limit position through a zero speed position to the opposite limit position. Up to the mid point of the speed range the two sun gears rotate oppositely until both are stationary at the mid point and then both sun gears accelerate in unison to maximum clockwise rotation at the end of the range as indicated in FIG. 6. Throughout this second forward speed range, the second sun gear S and the second set of planet gears 52 rotate freely without transmitting torque.

As indicated in FIG. 6, the two sun gears S and S and the ring gear 42 all rotate clockwise at the same maximum speed at the upper end of the second speed range. Therefore a transition to the higher third forward speed range may be carried out without interruption in torque output by simply operating clutches D and B in overlapping sequence. As indicated in FIG. 6, with clutches B and C engaged at the start of the. transition, clutch D is also engaged early in the transition. Later in the transition clutch B is disengaged to leave clutches C and D engaged for the third forward speed range. During this transition in which the output from the second motor-pump 34 is transferred by clutch operation from sun gear S to sun gear S the temporary simultaneously engagement of clutches B and D temporarily locks up the planetary gearing and the planetary gearing rotates as a unit with no relative rotation among its components.

With the second sun gear S rotating clockwise at maximum speed at the beginning of the third forward speed range, the volumetric displacement of the first motor-pump is gradually reduced to decelerate the rotation of the second sun gear S to zero at the mid point of the range as indicated in FIG. 6. Then for the second half of the third speed range the cylinder block of the first motor-pump 32 is swung past center in the opposite direction to accelerate the second sun gear S from zero speed to maximum speed in counterclockwise direction.

The manner in which the vehicle speed is increased in the third speed range may be understood when it is considered that the input shaft 30 imparts speed through the ring gear 42 to the first set of planet gears 45 for transmission by the planet gears 45 to the planet gear carrier 44 and at the same time the hydraulic drive unit in driving the second sun gear S imparts additional speed to the first set of planetary gears 45 through the second set of planetary gears 52. Thus, the first set of planetary gears 45 imparts the sum of the two speeds to the planet gear carrier 44.

FIG. 5 shows how the transmission may be employed in a different manner for high speed reverse operation. The connections in FIG. 5 provide less output torque for reverse speed than the connections shown in FIG. 2 but permit the reverse speed range to be extended. With the second motor-pump 34 stationary because the first motor-pump 32 is adjusted for zero displacement, the output shaft 54 is stationary. Clutch B is engaged to connect the stationary second motor-pump 34 to the stationary first sun gear S and clutch D is engaged to connect the stationary second motor-pump additionally to the stationary second sun gear S Consequently the planetary gearing is locked up to rotate as a unit. The cylinder block 36 of the first motor-pump 12 is then swung from its zero speed position to cause reverse acceleration of the second motor pump 34, which reverse acceleration is transmitted through the locked planetary gearing to the output shaft 54.

THE BASIC CONCEPT OF THE CONTROL SYS- TEM An important teaching of the invention is that the preparation of the graph shown in FIG. 6 is a basic approach to the development of suitable program means for an automatic control system. Since the heavy line or curve, designated 70, represents the required adjustments of the hydraulic drive unitover the series of speed ranges, a first program means may comprise essentially a programmer in the form of a program cam of a configuration corresponding to the configuration of curve 70 to carry out the sequential adjustments of the hydraulic drive unit. A second program means may comprise a programmer in the form of a suitable commutator valve synchronized with the cam to carry out the sequential operation of the clutches.

The operator may manipulate a single master control through a series of ranges of positions corresponding to the speed ranges of the transmission with the two program means following the changes in positions of the master control. In the preferred practice of the invention the master control is freely movable in complete independence of the two program means and suitable servo means causes the two program means to seek adjustments corresponding to the instant positions of the master control. In addition the preferred control system incorporates suitable means to control the rate at which the two program means respond to the master control, the servo means functioning with a delayed action that limits the rate at which the vehicle may be accelerated by the control system.

The invention also takes advantage of the fact that the portion of the curve 70 in FIG. 6 that lies within the forward speed range I is also applicable to the high speed reverse range. Accordingly, a feature of the invention is that the corresponding portion of the program cam is employed both for the first forward speed range and for the high speed reverse range. Thus FIG. 6 indicates by a dotted line how clutch D may be used along with clutch B for high speed reverse.

FIG. 7 is a fragmentary face view of a rotary program cam, generally designated 71, having a working surface a that conforms in configuration to the curve 70 of FIG. 6. In FIG. 7 the dotted line 72 indicates the minimum radius of the working surface 70a which corresponds to the maximum clockwise rotation of a sun gear; the dotted line 73 is the intermediate radius that corresponds to zero speed of a sun gear; and the dotted line 74 is the maximum radius that corresponds to maximum speed counterclockwise rotation of a sun gear. It can be seen in FIG. 7 that from the point 75 of the cam surface that corresponds to zero vehicle speed the cam drops to the minimum radius 72 at the outer limit of the low speed reverse range and in the other direction climbs to the maximum radius 74 at the upper end of the first forward speed range. Thus the slope of the cam surface 70a in FIG. 7 corresponds to the slope of the line 70 in these two speed ranges in FIG. 6.

The cam has a dwell 76 at its outer radius 74 which corresponds to the transition in FIG. 6 between range I and range II, the dwell providing a time-interval for the required overlapping operation of clutches. From the dwell 76 the cam surface drops back to the minimum radius 72 at the end of the second speed range and a second dwell 78 on the minimum radius 72 provides the transition shown in FIG. 6 between the second and third speed ranges. In the third speed range the cam surface 700 climbs from the minimum radius 72 to the maximum radius 74 in accord with the required change in speed of the second sun gear S in the third speed range in FIG. 6.

STRUCTURE OF THE PREFERRED EMBODI- MENT OF THE CONTROL SYSTEM The construction of the presently preferred embodiment of the control system may be understood by referring to FIGS. 8 21. FIG. 8 shows a manually operable master control 80 and associated linkages that connect the master control to the control system package. The master control 80 is in the form of a handle that combines the functions of a gear shift means and a speedratio control means. The handle 80 extends through a panel 81 adjacent the operators seat, the panel being formed with suitable slots that determine the paths of movement of the handle.'The handle is shown at a central neutral position in a transverse slot 82, at which position the vehicle is in free wheeling. FIG. 8 shows in perspective the panel 81 as viewed, not from the operators seat, but from a view point well forward'of the operator. Thus right and left as viewed in the perspective are the reverse of right and left as viewed by the operator. To avoid confusion the small diagram in the upper right hand corner of FIG. 8 shows the pattern of slots in the panel as viewed by the operator and hereafter the terms right and left will refer to this small diagram and similar small diagrams in FIGS. 12 21.

When the handle is moved to the right end of the transverse slot 82 it is in at a zero speed position from which it may be moved forward in a forward slot 84 through the forward speed ranges I, II and III or from which it may be moved rearward through a rearward 

1. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer connected to the first programmer to program the operations of the clutches through the series of ranges of vehicle speed, said master control being movable independently of said program means; and means responsive to the master control to urge the program means to positions corresponding to the instant positions of the master control with permitted lag in the movement of the program means.
 2. A combination as set forth in claim 1 which includes means to control the rate of movement of the program means.
 3. A combination as set forth in claim 1 in which said means to control the rate is connected to the master control.
 4. A combination as set forth in claim 1 in which said master control is manually movable independent of the program means; and which includes means to cause the program means to follow the movements of the master control.
 5. A combination as set forth in claim 4 which includes means directly connected to the program means to control the rate of movement of the program means.
 6. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means movable in response to said master control through a series of ranges of movement corresponding to said sEries of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer correlated with the first programmer to program the operations of the clutches through the series of ranges of vehicle speed, said master control being manually movable independent of the program means; and means to cause the program means to follow the movements of the master control, said means to cause the program means to follow the movements of the master control comprising a lost-motion connection between the master control and the program means together with spring means stressed by the lost-motion connection to urge the program means to positions corresponding to the instant positions of the master control.
 7. A combination as set forth in claim 6 in which said means to cause the program means to follow the movements of the master control comprises: an input member operatively connected to the master control for movement therewith; an output member operatively connected to the program means for operation thereof; and servo means operatively connected to the output member, said servo means being responsive to the input member to cause the output member to seek positions corresponding to the instant positions of the input member.
 8. A combination as set forth in claim 7 which includes means to control the rate of response of the output member to changes in position of the input member.
 9. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means movable in response to said master control through a series of ranges of movement corresponding to said series of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer correlated with the first programmer to program the operations of the clutches through the series of ranges of vehicle speed, and motion-amplifying means to increase the range of movement of said program means relative to the range of movement of the master control.
 10. A combination as set forth in claim 1 in which said fluid-pressure-actuated adjustment means comprises a cam responsive to the master control and fluid-pressure-actuated means controlled by the cam to vary the adjustment of the hydraulic drive unit.
 11. A combination as set forth in claim 10 which includes servo-positioner means having an input member and an output member, said input member being operatively connected to the master control for simultaneous movement therewith, said output member being connected both to said second programmer and to the cam for actuation thereof.
 12. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means mOvable in response to said master control through a series of ranges of movement corresponding to said series of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer correlated with the first programmer to program the operations of the clutches through the series of ranges of vehicle speed, said master control being movable forwardly along a first path from a zero-speed position to advance through forward speed ranges, said master control being movable rearwardly along a second path from a zero-speed position to advance through a reverse speed range, said fluid-pressure-actuated adjustment means comprising a cam responsive to the master control and fluid-paessure-actuated means controlled by the cam to vary the adjustment of the hydraulic drive unit, a portion of the cam being movable in a given direction both to advance through a given forward speed range and to advance through said reverse speed range; and means to move said cam in said given direction both in response to advance of the master control forwardly through said given forward speed range and in response to advance of the master control rearwardly through said reverse speed range.
 13. A combination as set forth in claim 6 which includes motion-reversing gearing and which includes means to make said motion-reversing gearing effective between the master control and the cam in response to shifting of the master control from said first path to said second path.
 14. A combination as set forth in claim 13 in which said second programmer and said cam are interconnected for simultaneous movement so that a portion of the movement of the second programmer corresponds to said portion of the cam; in which clutches for said given forward speed range are responsive to movement of the master control into and out of said first path; and in which clutches for said reverse speed range are responsive to movement of the master control into and out of said second path.
 15. A combination as set forth in claim 14 in which said second programmer is a control valve; in which said clutches are operated by fluid pressure; in which fluid-pressure-actuated clutch valves supply fluid pressure to the clutches selectively; in which said clutch valves are responsive to changes in adjustment of said control valve; and which includes means to change the responsiveness of the clutch valves to the control valve in response to shift of the master control from said first path to said second path.
 16. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means movable in response to said master control through a series of ranges of movement corresponding to said series of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer correlated with the first programmer to program the operations of the clutches through the series of ranges of vehicle speed; two clutches for power flow from the hydraulic drive unit to the planetary gearing for a first forward speed range, both of said clutches being operable by fluid pressure; a source of fluid pressure to actuate the two clutches; and meanS to cut off said source from one of the two clutches when said master control is positioned at its neutral position thereby to ensure that the vehicle is in free wheeling when the master control is at its neutral position.
 17. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination: a manually operable master control movable through a series of ranges of movement corresponding to said series of ranges of vehicle speed; program means movable in response to said master control through a series of ranges of movement corresponding to said series of ranges of vehicle speed, said program means including a first programmer to program the adjustments of the hydraulic drive unit through the series of ranges of vehicle speed, said program means including a second programmer correlated with the first programmer to program the operations of the clutches through the series of ranges of vehicle speed; a first piston included in said fluid-pressure-actuated adjustment means to advance to adjust the hydraulic drive unit in one respect; a second piston included in said fluid-pressure-actuated adjustment means to advance to adjust the hydraulic drive unit in the opposite respect; two springs to urge the two pistons respectively to advance; stop means to terminate the pressures of the two springs respectively when the hydraulic drive unit is at neutral adjustment; a four-way valve to control the application of fluid pressure to the two pistons thereby to control the adjustment of the hydraulic drive unit; and means responsive to the master control to control said valve to cause adjustments of the hydraulic drive unit to follow the movements of the master control.
 18. A control system for a vehicle that is driven by an engine through a transmission that includes planetary gearing and also includes a hydraulic drive unit that is adjustable for variably and reversibly driving a reaction component of the planetary gearing through a series of ranges of vehicle speed, the transmission further including clutches for activating gear trains for the series of ranges, said control system having in combination; a manually operable master control movable through ranges of movement corresponding to the ranges of said series of ranges of vehicle speed, said master control being movable in one direction from a given position through a forward speed range and being movable from the given position in the opposite direction through a reverse speed range, cam means operatively responsive to the movements of said master control, said cam means having a control surface of a profile corresponding to a graph of the changes in adjustment of the hydraulic unit through said ranges of the series of ranges of vehicle speed, said control surface of the cam having a point corresponding to said given position of the master control such control surface of the cam progressively changing in elevation in one respect in one direction from said point for said forward speed range and progressively changing in elevation in the opposite respect in the opposite direction for said reverse speed range, means to vary the adjustments of the hydraulic drive unit; follower means cooperative with said control surface of the cam and operatively connected to said adjustment-varying means to program the adjustments of the hydraulic drive unit through said ranges of the series of ranges of vehicle speed; and means responsive to movements of the master control to program the operation of the clutches through said ranges of the series of ranges of vehicle speed, two of said clutches being engaged for both said forward speed range and said reverse speed range, whereby the master control may be gradually shifted forwardly and rearwardly from its zero-speed position to inch the vehicle forwardly through said forward speed range and rearwardly through said reverse speed range without disengaging said two clutches.
 19. A combination as set forth in claim 18 in which the master control is movable laterally from said zero-speed position to release one of said two clutches to place the vehicle in free wheeling.
 20. A combination as set forth in claim 19 in which said two clutches connect the hydraulic drive unit to two different components of the planetary gearing.
 21. A combination as set forth in claim 18 in which the master control is operatively connected to the cam means by motion-amplifying means.
 22. A combination as set forth in claim 18 which includes servo-positioning means having an input member and an output member; in which motion-amplifying means operatively connects said follower to said input member; and in which the output member is operatively connected to said adjustment-varying means.
 23. A combination as set forth in claim 18 in which said control surface of the cam includes dwells for pauses in the operation of said adjustment-varying means at transitions between successive ranges of speed to permit changing the clutches during the transitions.
 24. A combination as set forth in claim 23 in which the means to program the operation of the clutches is constructed and arranged for overlapping operation of the clutches during the transition periods. 